mongodb / mongoose聚合结合了两个表/集合

Question

I am using mLab for database and mongoose in node js.I am using swagger which should not cause any problem. I have following schemas. when user request, I need to return movie and review together if (review = true) in query. One movie may have multiple reviews. first, I have to find all the movies in the database. when I find movies, I have to go through each of them, look for any reviews in another database and somehow attach them in movie. I need to return all the movies in one package because it will be used in getAll fucntion. No matter what I do it only returning movies without reviews.

 var mongoose = require('mongoose'); var reviewSchema = new mongoose.Schema({ movie: {type: String, required: true}, reviewer: {type: String, required: true}, rating: {type: Number, required:true, min: 1, max: 5}, text: {type: String, required: true}, }) var movieSchema = new mongoose.Schema({ Title: {type: String, required: true, unique: true}, YearReleased: {type: Number, required: true}, Actors: [{ Name: {type: String, required: true} }] }) 

.

 function getAll(req,res,next){ db.Movies.find({},function(err,movies){ if(err) throw {err:err}; if(req.swagger.params.review.value === false) res.send({Movielist: movie}); else { movies.forEach(function(movie, index){ db.Reviews.find({movie:movies[index].Title}, function (err, review) { if(err) throw {err:err} movies[index].Review = review // I am trying to populate each movie with reviews }); }); res.send({Movielist: movies}); } }); } 

Answer 1

res.send is called before the db reviews result is received:

        movies.forEach(function(movie, index){
            // this call is asynchronous, res.send will run before the callback
            db.Reviews.find({movie:movies[index].Title}, function (err, review) {
                if(err) throw {err:err}
                movies[index].Review = review    // I am trying to populate each movie with reviews
            });
        });
        res.send({Movielist: movies});

You can use promises to wait for the results. I'll give an example with async/await. Using promises without async/await is also an option.

async function getAll(req,res,next) {
  try {
    let movies = await getMovies();
    res.send(movies);
  } catch (err) {
    console.log(err.stack);
  }
}

async function getMovies () {
  return new Promise(function (resolve, reject) {
    db.Movies.find({},function(err,movies){
      if(err) reject(err);
      if(req.swagger.params.review.value === false)
          resolve({Movielist: movie});
      else {
        movies.forEach(function(movie, index){
          let review = await getReviews();
          movies[index].Review = review
        });
        resolve({Movielist: movies});
      }
    });
  });
}

async function getReviews (movie, index) {
  return new Promise(function (resolve, reject) {
    db.Reviews.find({movie:movies[index].Title}, function (err, review) {
        if(err) reject({err:err});
        resolve(review);
    });
  });
}

This could need some tweaks as I have not tested it. I hope it gives the general idea of how to fix the issue.

Without async/await you can call the promises and run ".then" to process the results. If you haven't used promises a few google searches should help understand how .then works.

Answer 2

First thank you @curtwphillips however, I have found short way to do this. But for this to work, movie and review have to in same database as different collection. If you use different database, it doesn't work

 function getAll(req,res,next) { if (req.query.review === 'true') { db.Movies.aggregate([ { $lookup: { from: "reviews", localField: "Title", foreignField: "movie", as: "review" } } ], function (err, result) { if (err) throw {err: err}; else { res.send({Movielist: result}); } }); } else { db.Movies.find({}, function (err, movies) { if (err) throw {err: err}; res.send({Movielist: movies}) }) } }